1. Field of the Invention
The present invention relates generally to improvements in saws, and more particularly, pertains to new and improved oscillatory saws of the type used for cutting plaster casts, bone and the like.
2. Description of the Prior Art
In the field of oscillatory saws, it has been the practice to employ an oscillating mechanism to convert rotary motion to the oscillatory motion of the cutting blade of the saw. These devices although functioning satisfactorily have been unsatisfactory in that they make a continuous loud and frightening sound when operating. This sound is present without any sawing activity. The sound tends to terrify children and causes even strong adults to have moments of panic. The blade of a cast-cutting saw is typically a thin blade of steel two inches in diameter with saw teeth on the periphery. It differs from an ordinary radial saw in that the blade does not rotate. Instead the blade simply oscillates. It moves a short distance in the clockwise direction then reverses and goes a similar distance in a counterclockwise direction. A typical distance of movement is 0.05 inches on the periphery. However, this can vary. The purpose of the oscillating movement is so that the blade will not cut skin. As it touches skin, which is resilient, the skin moves back and forth with the saw teeth without being cut or ruptured. However, when coming into contact with cast material, which is hard and brittle, the blade cuts and breaks away the cast material as the blade oscillates against it. This is also true when the blade oscillates against bone material.
The oscillating mechanism used by the prior art causes the loud noise made by the prior art saws. Typical arrangements involve a motor rotating a ball bearing mounted on an eccentric shaft which moves within a metal fork, knocking it first in one direction and then in the other. The saw blade shaft is pinned at the other end of the fork and is oscillated back and forth. This kind of structure is illustrated in U.S. Pat. Nos. 2,427,580 and 4,252,121.
Other oscillatory saw structures which utilize cams and cam followers are illustrated in U.S. Pat. Nos. 3,044,171 and 3,952,412.